Directional antenna system



Sept. 9, 1941.

H. SCH USTER DIRECTIONAL ANTENNA SYSTEM Filed May 29, 1940 A )FIN scuTER FIG.| FIG.2

l L 32 J FiG.3

l 46 5 INVENTOR Patented Sept. 9, 1941 UNITED 2,255,520 DIRECTIONALANTENNA SYSTEM Hermann Schuster, Berlin-Zehlendorf, Germany,

G. in. b. 11., Berlin-Zehlenassignor to Fernseh dorf, GermanyApplication May 29, 1940, Serial No. 337,909 In Germany May 13, 1939 4Claims.

This invention relates to a directional antenna system and particularlyto a system for simultaneously receiving signals of widely differingwave lengths.

For the reception of signals of relatively short wave lengths, such astelevision signals, it is often desired to provide a directionalantenna, particularly if the receiver is located between two stationsoperating with the same wave length. Since it is generally necessary toerect an outside antenna for the reception of television signals, it isdesirable to make use of such an antenna also for the reception ofsignals of relatively long wave length, such as conventional soundbroadcast signals. Furthermore, it can also be of advantagesimultaneously to employ the same antenna system for reception ofsignals of short and long wave lengths.

The object of the present invention, therefore, is to provide a new andimproved'antenna system which has a directional effect for signals ofrelatively shortwave length and which can be used for simultaneousreception of signals of both relatively short and relatively long wavelengths.

In accordance with the present invention,

there is provided a receiving antenna system comprising a firsthalf-wave length rod for intercepting radiated signals of relativelyshort wave length, and a second half-wave length rod disposedsubstantially parallel to the first rod and spaced substantiallyone-quarter wave length therefrom for reflecting the radiated signals.Additional means are provided for conducting the intercepted signals toa signal-reproducing means.

i In accordance with another feature of the present, invention, thereare provided similar antenna systems intercepting signals of both rela-,tively short Wave length and relatively long wave length and a singlemeans for conducting the intercepted signals. Further means are provi dfor separating the conducted signals and for separately' applying theseparated signals to signalreproducing means.

For a better understanding of the invention, together with other andfurtherobjects thereof, reference is had to the following description,taken in connection with the accompanying drawing, and its scope will bepointed out in the appended, claims.

' point is mismatched In the accompanylng drawing, Fig. 1 shows aschematic diagram of an antenna system embodying the present invention,while Fig.2 shows a modification thereof and Fig. 3 schematically showsa circuit for separating the signals of short and long wave lengths.

Referring now more particularly to Fig. l of the drawing, there is shownschematically a receiving antenna system comprising a solid conductingrod I- having a length substantially equal to one-half the wave lengthof the short Wave signal tov be received. A similar rod 2 ofsubstantially equal length is. disposed parallel thereto. and spacedfrom thefirst rod by one-quarter wave length. Both rods are supported bya supporting means 3 of insulating material which is attached to ametallic antenna mast 4. .Attached to the antenna mast 4 andelectrically connected thereto is a metallic housing 5 preferablydisposed in the vicinity of the-lower ends of the rods l and 2, as shownin the drawing.

For the purpose of conducting signals intercepted by the antenna rods. Iandv 2 to the signalreproducing apparatus, there is provided aconcentric cablefi disposed within the hollow of the antenna mast 4, asshown. The outer conductor of the cable 6 is preferably connected toground at the signalereproducing apparatus, as schematically indicatedat 1. For reception of signals of relatively short wave length, theinner conductor of cable 6 is conductively connected to a point 8 of therod 1 by way of the inner conductor of a concentric cable 9, Whose outerconductor and shield is conductively connected to the metallic housing5. For reception of signals of relatively long wave length, the innerconductor of the cable 6. is also connected to a point It) on theantenna rod 2 by way of a first de-coupling resist.- or H, a matchingtransformer i2, and a second de-coupling resistor 13.

v In operation, signals of relatively short wave length are interceptedby the antenna rod l and conducted to the inner conductor of the cable tI by way of the concentric cable 8, whose inner conductor is connectedto the rod 1 at the point 8. The position of point 8 is preferablysochosen.

of the antennarod at. that with respect'to the characteristic impedanceof the cable 6 by an amount greater than 1 to 3, preferablyapproximately I to i. For a diameter of 22 millimeters for the rod I, asignal wave length of 2.92 meters and a characteristic impedance of thecable 6 of ohms, a preferred position of the point 8 for favorableside-band frequency response is 770 millimeters from one end of the rodl. o

For signals of relatively short wavelength, the antenna rod2 issubstantially unloaded, as

that the impedance will be explained later, and therefore oscillatesfreely at this wave length. Hence, all signals arriving thereat in thedirection from rod I toward rod 2 will be reflected by rod 2 with such aphase relation with respect to the oncoming wave, due to thequarter-Wave length spacing between rods I and 2, that the oncoming waveand the reflected wave will cancel each other. Thus, the rod I receivesonly signals which come in the direction from the rod 2 toward rod. I.

For signals of relatively long wave length, the rod 2 cannot oscillatefreely, wherefore these signals are intercepted and conducted to theinner conductor of cable 6 by way of the decoupling resistor I3,matching transformer I2 and de-coupling resistor II. For short wavelengths, the value of the ole-coupling resistor I3.

must be large compared with the impedance of the reflector rod 2 at thepoint I0, so that the rod 2 may be permitted to oscillate freely at'those wave lengths. On the other hand, the value of the resistor I3preferably should be small compared with the input impedance of thetransformer I2 as seen from the rod 2 to prevent substantial attenuationof the long wave signals applied to the transformer. Furthermore, it isthen possible to use a standard commercial transformer, since arelatively low value of the resistor I3 does not considerably shift thefrequency pass-band of the matching transformer. The value of thede-coupling resistor II must be small compared with the capacitivereactance of the cable 6 for sound broadcast frequency, so as notunnecessarily to attenuate these signals, and large compared with thecharacteristic impedance of this cable, so as not to load the rod I withthe matching transformer I2.

In this circuit connection, the antenna rod I receives signals ofrelatively short wave length coming in the direction of rod 2 toward rodI, and the intercepted signals are conducted to the concentric cable 5.The rod 2 oscillates freely at the short wave length and reflectssignals coming in the direction from rod I toward rod 2 in such a phasethat the oncoming and the reflected signal waves cancel each other. Therod 2 also serves as a receiving antenna for signals of comparativelylong wave length which are also applied to the concentric cable 6 by wayof the resistors II and I3, and the matching transformer I2.

Fig. 2 shows a modification of the antenna system just described. Inthis system there is again provided a solid conducting rod ofsubstantially one-half wave length. A similar rod 2I of substantiallyequal length is disposed parallel thereto and spaced from the first rodby onequarter wave length. Both rods are supported by a supporting means23 which is attached to the upper portion 24 of a metallic antenna mast25. The rod 2! is conductively connected to the supporting means 23,while the rod-20 is insulated therefrom by means of an insulator 22.Attached to the antenna mast 25 and electrically connected thereto, is ametallic housing 26 from which the upper portion 24 of .the antenna mastand the supporting means 23 are insulated by means of an insulator 21.The housing 26 is preferably disposed in the vicinity of the lower endsof the rods 20 and 2|, as shown in the drawing.

For the purpose of conducting signals intercepted by the antenna rods 20and 2I to the signal-reproducing apparatus, there is again provided aconcentric cable 28 disposed Within the hollow of the antenna mast 25,as shown. The

outer conductor of the cable 28 is preferably connected to ground at thesignal-reproducing apparatus, as schematically indicated at 29. For thereception of signals of relatively short Wave length, the innerconductor of cable 28 is conductively connected with a point 36 on therod 26 by way of the inner conductor of a concentric cable 3|, whoseouter conductor and shield is conductively connected to the metallichousing 26. For the reception of signals of relatively long wave length,the inner conductor of the cable 28 is also connected to the center ofthe antenna rod 2I by way of a de-coupling resistor 32, a transformer33, the upper portion 24 of the antenna mast, and the supporting means23.

As can be seen readily by comparing Figs. 1 and 2, the only differencebetween the structures illustrated therein is that the transformer 33 ofFig. 2 is directly coupled to the center of the rod 2!, at which pointthe impedance of this rod is substantially zero for signals of shortWave lengths. Hence, the impedance of the transformer 33, when viewedfrom rod 2 I, always represents a value greater than Zero for the shortwave signals and therefore makes superfluous the provision of ade-coupling resistor, otherwise necessary to permit the rod 2! tooscillate freely at the short wave lengths. In order to preventoscillations from being developed in the supporting structures of therod 2|, it is preferable to make the effective length of the upperportion 24 of the antenna mast equal to one-quarter of the short wavelength.

The operation of the system illustrated in Fig. 2 is substantially thesame as that of Fig, 1, inasmuch as the rod 20 intercepts signals ofrelatively short wave length which are conducted to cable 28, while therod 26 is permitted to oscillate freely and serves as a reflectorcancelling all signals arriving in the direction from rod 25 toward rod2 I and simultaneously serves to intercept signals of relatively longwave length which are also conducted to the cable 28.

Fig. 3 schematically illustrates the receiving station proper, wherethere is provided a grounded metallic housing 40 into which is insertedthe end of a concentric cable 4|, whose outer confductor and shield isconductively connected therewith. This cable 4| may be identical withcables 6 or 28 of Figs. 1 and 2, respectively. The inner conductor ofcable M is connected to the antenna terminal of a receiving andreproducing apparatus for short wave signals, such as receiver 42, byway of a coupling condenser 43, in order to apply relatively short wavesignals thereto. The inner conductor of cable 4| is also connected tothe input terminal of a receiving and reproducing apparatus for longwave signals, such as sound broadcast receiver 44, by way of a de-coupling resistor 45 and a matching transformer 46, in order to applyrelatively long wave signals thereto. In order to obtain properseparation of the signals of relatively short and relatively long wavelengths, the capacitive reactance of the condenser 43 for the short wavesignals is preferably chosen to be much smaller than the impedance ofthe de-coupling resistor 45, while the value of the latter should besmall compared with the input impedance of the transformer 46, in orderto prevent undue attenuation of the long wave length signals.

Hence, a system comprising the apparatus shown in Figs. 1 and ,3 or 2and 3, respectively, is

- adapted to receive signals of relatively short wave length from onedirection only and simultaneously to receive signals of relatively longwave length from any direction, to conduct such signals over a singlemeans, and to separate such signals at the end of this conducting meansso that they may be applied to separate signalreproducing apparatus.

While there has been described what is at present considered thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A receiving antenna system comprising a first half-wave length rodfor interceptingiradiated signals of relatively short wave length, asecond half-wave length rod substantially parallel to said first rod andspaced substantially one-quarter wave length therefrom for reflectingradiated signals of a relatively short wave length and interceptingradiated signals of a relatively long wave length, a single means forconducting intercepted signals of said relatively short and long wavelengths from said first and second rods, means for separating saidconducted signals, and means for separately applying said separatedsignals to signal-reproducing means.

2. A receiving antenna system comprising a first half-wave length rodfor intercepting radiated signals of relatively short wave length, asecond half-wave length rod substantially parallel to said first rod andspaced substantially one-quarter wave length therefrom, adapted tooscillate freely at said relatively short wave length and forintercepting radiated signals of a relatively long wave length, a singlemeans for conducting intercepted signals of said relatively short andlong wave lengths from said first and second rods, means for separatingsaidv conducted signals, and means for separately applying saidseparated signals to signal-reproducing means.

3. A receiving antenna system comprising a first half-wave length rodfor intercepting radiated signals of relatively short wave length, asecond half-wave length rod substantially parallel to said first rod andspaced substantially one-quarter wave length therefrom for reflectingradiated signals of a relatively short wave length and interceptingradiated signals of a relatively long wave length, a single means forconducting signals, first means for coupling said first rod to saidsignal-conducting means, second means for coupling said second rod tosaid signal-conducting means, said last-named means adapted to passsignals of relatively long wave length only, first de-coupling meansconnected between said second coupling means and said second rod, secondde-coupling means connected between said second coupling means and saidsignal-conducting means, means for separating said conducted signals,and means for separately applying said separated signals tosignal-reproducing means.

4. A receiving antenna system comprising a first half-wave length rodfor intercepting radiated signals of relatively short wave length, asecond half-wave length rod substantially parallel to said first rod andspaced substantially one-quarter wave length therefrom for reflectingradiated signals of a relatively short Wave length and interceptingradiated signals of a relatively long Wave length, a single means forconducting intercepted signals of said relatively short and long wavelengths from said first and second rods, means for conductivelyconnecting said lastnamed means to the center point on said second rod,means for separating said conducted signals, and means for separatelyapplying said separated signals to signal-reproducing means.

HERMANN SCHUSTER.

